Numerous studies indicate that neuropeptide growth factors contribute to the development and progression of prostate cancer. Neutral endopeptidase 24.11 (NEP, CALLA, CD10) is a cell-surface peptidase that inactivates a variety of neuropeptides implicated in prostate cancer, including bombesin, endothelin-1 (ET-1) and neurotensin. We first reported that NEP expression is decreased in a subset of primary and metastatic prostate cancers, and that NEP expression is in part regulated by androgen and decreases with androgen-withdrawal. In our research over this past grant period, we have characterized the androgen regulation of the NEP gene, demonstrated that replacement of NEP using either exogenous recombinant NEP or overexpression of cell-surface NEP inhibits prostate cancer cell growth, cell migration and tumorigenicity, and have identified at least three distinct mechanisms by which NEP exerts a tumor suppressive effect, including 1) catalytic inactivation of NEP's neuropeptide substrates, 2) indirectly associating with phosphatidylinositol 3-kinase (P13-K) protein and inhibiting the interaction of P13-K with focal adhesion kinase (FAK), and 3) directly associating with and stabilizing the PTEN tumor suppressor gene protein. These data suggest that the NEP protein normally functions to regulate prostate epithelial cell growth, and that loss of NEP expression may contribute to prostate cancer growth and progression. In this renewal application, we propose to continue to define the mechanisms of NEP anti-tumor effects in prostate cancer cells, to more thoroughly decipher the regulation of NEP expression, and to study the potential of NEP as therapy using a novel fusion protein in which NEP is linked to a monoclonal antibody which specifically targets prostate cancer cells. These proposed studies should provide significant new knowledge on the multiple functions of cell-surface peptidases with NEP as a prototype, and more clearly define the involvement of NEP in the development and progression of prostate cancer.